A variety of diagnostic techniques utilize a cell count from a fluid sample, such as a differential white blood cell count. For example, a differential white blood cell count may be utilized in medical diagnostic techniques for detecting sepsis, leukemia, AIDS, radiation exposure, as well as other conditions. Typical methods for measuring white blood cell count include flow cytometry, electrical impedance counting, and visual counting from a fluid sample under a microscope. See, for example, Holmes, D., et. al. “Leukocyte analysis and differentiation using high speed microfluidic single cell impedance cytometry,” Lab Chip 9, 2881-2889 (2009), which article is hereby incorporated by reference in its entirety for any purpose. These commonly used techniques may require a large fluid sample for analysis, and may occur as a stand-alone diagnostic procedure. Further, the techniques may require operation by a skilled technician.
Microfluidic systems, including “lab on a chip” or “lab on a disk” systems continue to be in development. See, Lee, B. S., et. al., “A fully automated immunoassay from whole blood on a disc,” Lab Chip 9, 1548-1555 (2009) and Madou, M. et. al., “Lab on a CD,” Annu. Rev. Biomed Engr. 8, 601-628 (2006), which articles are hereby incorporated by reference in their entirety for any purpose.